The aim of this project is to study mechanisms of immunity and immune evasion in schistosomiasis with the ultimate goal of developing an experimental vaccine employing defined antigens. A. Vaccination trials with purified paramyosin and GST. Paramyosin and glutathione-S transferase (GST) were both shown to induce protective immunity in mice using either BCG or saponin as adjuvants, while combining the two antigens had no additive effect. B. Recognition of paramyosin by endemic population. Patients in a Brazilian field population were screened for antibodies against paramyosin. Asymptomatic, non-infected individuals were found to develop higher responses than infected patients while hepatosplenic patients developed lower response on average than either group. C. Characterization of non-paramyosin T cell protective immunogens. Non-paramyosin molecules which could serve as immunogens for protective immunity were characterized using T cell immunoblotting and chromatographic techniques. D. Role of antibodies against Sm-200 in praziquantel therapy. In passive transfer studies a monoclonal antibody against a 200 kD tubercle glycoprotein was shown to restore the ability of u- suppressed mice to eliminate adult worms when treated with praziquantel.